1. Field of the Invention
The invention relates in general to a power supply device, and more particularly to a power supply apparatus maintaining its output power signal with the assistance of another power supply.
2. Description of the Related Art
Integrated circuit memory technology continues to evolve toward smaller and smaller geometries. While reductions in channel-lengths and gate-oxide thicknesses in metal-oxide-semiconductor memories can be used in low power system.
Data in memories must be read out in a short time. Thus, the word line is selected and is applied a high voltage to read the memory data. In general, there are two methods to generate high voltage power in the low power system. First method is using boost circuit. A high voltage power can be obtained rapidly by using boost circuit method, but it will take a huge die area and produce a big power noise bounce. The other method is using the charge pump circuit. The charge pump method takes smaller die area then the boost method, so do the power noise.
In some operation condition, the charge pump circuit must apply a high voltage to a specific substrate or word line to make the function correct. In a low power system, the charge pump circuit constructs more stages to supply a predetermined high voltage. In this situation, the charge pump will spend more time to build up internal voltage.
When a read function is executed, all data line pass gates are applied a system power to pass memory data to sense amplifier. In a low power system, the memory drain side will apply a voltage about 1V for reading data. Thus, the memory data will pass through all data lines' pass gates to the sense amplifier to determine whether memory data is 0 or 1. Unfortunately, the read out data signal will be suppressed because all pass gate voltages are not enough to fully pass the data signal. The sense amplifier may receive a wrong data signal. It will suffer a read problem.